ProjectSummary Animals interact with members of their own or other species in the context of social and defensive behaviors,predator-preyrelationshipsandsymbioses.Inallsuchcontexts,executionoftheappropriate kind of interaction depends on a sensorimotor pathway that transduces information about another organismandgeneratesabehavioralresponse.Coreprinciplesofsuchsensorimotorpathwaysremain mysterious, including how representations of other animals are constructed in the brain based on multisensory information, and how such neural representations are appraised by decision-making circuitrytoselecttheappropriateaction.Imagingneuralactivityinbehavinganimalsoffersthepotential to make breakthroughs in the mechanistic understanding of how animals interact. In particular, generalizable insights into sensorimotor processing may come from model species with small, minimallycomplexbrainsthatareneverthelesscapableofexecutingcomplexbehavioralinteractions. Current small-brained model systems, however, have an inherent limitation in that they must be physicallyrestrainedforbrainimaging?aprocedurethatstronglyrestrictstheircapacitytoengagein behavioralinteractions.Toovercomethisproblem,toolsforbehavioralanalysisandbrainimagingwill bedevelopedforanovelinvertebratemodelwithaspecializedphenotypethatenablesittoretainits capacity to interact with other organisms even when tethered and head fixed for brain imaging. The rovebeetle,Dalotiacoriaria,possessesaflexibleabdomenthatisusedasanappendagetoengagein reproductive and aggressive interactions with conspecifics;? the abdomen also houses a targetable chemicaldefenseglandthatcanbeaccuratelytargetedtosecretenoxiousbenzoquinonesdirectlyonto heterospecific threats. The mode of deployment of the abdomen provides a direct readout of the sensorimotor processing that occurs when the beetle encounters different types of animal. In this proposal,aclosed-loopvirtualrealityplatformwillbeconstructedinwhichtetheredDalotia?sbehavior canbequantifiedusingmachinevisionasthebeetleinteractsinanaturalisticfashionwithrealorfictive animals. This platform will be used to experimentally deconstruct how Dalotia integrates different sensory modalities to build internal representations of other living organisms. Transgenic Dalotia will be created that express a genetically-encoded calcium sensor in defined brain regions. Combining thesetechnologies,functionalimagingofthebrainofDalotiawillbeachievedwhilethebeetleperforms naturalisticinteractionswithotherorganisms.Thisproposalwillbefoundationalforfurtherexploitation ofthismodelsystemtorevealhowsensorimotorprocessesenableanimalstointeract.